Reconstructing Early Atlantic to Early Subatlantic Peat-Forming Conditions

GEOLOGICA BELGICA (2018) 21/3-4: 129-142

Reconstructing Early Atlantic to Early Subatlantic peat-forming conditions of the ombrotrophic Misten Bog (eastern Belgium) on the basis of high-resolution analyses of pollen, testate amoebae and geochemistry Maurice STREEL1*, Marc PAILLET1, Jérémie BEGHIN1, Thomas LECLEF1, Mariusz LAMENTOWICZ2, Kamyar KAMRAN1, Mona COURT-PICON3, Mohammed ALLAN4, Nathalie FAGEL4, Philippe GERRIENNE1 1PPP, Département de Géologie, Université de Liège, Allée du 6 Août, B18, Sart Tilman, B-4000 Liège, Belgium. 2Laboratory of Wetland Ecology and Monitoring, Department of Biogeography and Paleoecology, Faculty of Geographical and Geological Sciences, Adam Mickiewicz University, Bogumila Krygowskiego 10, 61-680 Poznań, Poland. 3Earth and Life History Division, Archaeosciences Unit, Royal Belgian Institute of Natural Sciences, Rue Vautier 29, B-1000 Bruxelles, Belgium. 4AGEs, Département de Géologie, Université de Liège, Allée du 6 Août, B18, Sart Tilman, B-4000 Liège, Belgium. *corresponding author: [email protected].

ABSTRACT. A seven metres thick peat bog (Misten, Hautes-Fagnes, Belgium) has been studied at high resolution in order to reconstruct the conditions of peat formation and evolution on the basis of pollen, testate amoebae analysis, and geochemistry. The sampled section of the peat bog corresponds to the most part of the Atlantic period, all the Subboreal period and the earliest Subatlantic period, i.e. a time interval between 7300 cal BP and 2000 cal BP. The identification of tie-points in the pollen assemblages recognized in a previous work (Persch, 1950) performed in the periphery of the same peat-bog, allows accurate correlation of the two sites, 460 cm thickness of peat in the central part corresponding to 230 cm thickness of peat in the periphery. The well constrained dates of the tie-points in the present work provide a more precise chronology of the events identified in Persch’s pollen diagram. A comparison of pollen data in both sites demonstrates that, as expected, the Corylus pollen rain is proportionally more important and the Quercetum mixtum pollen rain proportionally less important in the central area of the peat bog than in the periphery. The study of the testate amoebae in the central part of the peat bog is the major contribution of the present work. A stratigraphically constrained analysis resulted in the identification of five biozones, the zonation being mainly built on the fluctuations observed between Archerella (Amphitrema) flavum and Difflugia pulex. Three transfer functions have been applied and compared. Coupled with the humification values of each level, it allows a very accurate approach of the water-table level, and hence of local climatic conditions, at the time of the peat formation. Combination of pollen results and testate amoebae zonal subdivisions allows the definition, dating and interpretation of 18 rather short time intervals with an approximate duration of 200 to 300 years each. Our results validate and expand a previously published climate interpretation that combined geochemical data and a preliminary testate amoebae analysis.

KEYWORDS: Misten peat-bog, Hautes-Fagnes, Atlantic, Subboreal, Subatlantic, pollen analysis, testate amoebae, geochemistry.

RÉSUMÉ. Reconstruire les conditions de formation de la tourbe entre l’Atlantique ancien et le Subatlantique ancien dans la tourbière du Misten (Est de la Belgique) sur la base d’analyses à haute résolution du pollen, des thécamoebiens et de la géochimie. La tourbière du Misten (Hautes-Fagnes, Belgique), épaisse de 7 mètres, a été étudiée avec pour objectifs la reconstitution de l’évolution de la tourbière et des conditions de la formation de la tourbe, à partir de l’analyse des grains de pollen et spores, des thécamoebiens, ainsi que de la géochimie. La partie étudiée de la tourbière représente une grande partie de la période Atlantique, l’entièreté de la période Subboréal et le début de la période Subatlantique, soit environ l’intervalle de temps compris entre 7300 cal BP et 2000 cal BP. La reconnaissance d’assemblages polliniques repères définis par un travail plus ancien (Persch, 1950), réalisé dans la périphérie de la même tourbière, permet de corréler étroitement entre eux les deux sites étudiés, 460 cm d’épaisseur dans la partie centrale de la tourbière correspondant à 230 cm d’épaisseur dans la périphérie. La datation précise des repères polliniques dans la séquence qui fait l’objet de ce travail permet d’obtenir une chronologie plus precise des événements reconnus dans le diagramme pollinique de Persch en 1950. La comparaison des données polliniques indique que, comme attendu, la pluie pollinique de Corylus est proportionnellement plus importante et celle du Quercetum mixtum, moins importante dans la partie centrale de la tourbière qu’à la périphérie de celle-ci. L’analyse des thécamoebiens dans la partie centrale de la tourbière constitue l’apport majeur du présent travail. Cinq biozones ont été identifiées par une analyse contrainte stratigraphiquement. La zonation obtenue est essentiellement basée sur les fluctuationsd’Archerella (Amphitrema) flavum et Difflugia pulex. Trois fonctions de transfert ont été appliquées et comparées. Couplée à la mesure du taux d’humification des niveaux concernés, elles permettent une analyse détaillée du taux d’humidité de la tourbe, et donc des conditions climatiques locales au moment de la formation de cette dernière. L’intégration des résultats polliniques dans la zonation basée sur les thécamoebiens permet de définir, de dater et d’interpréter 18 intervalles de temps relativement courts, de l’ordre de 200 à 300 ans chacun. Nos résultats valident et complètent une première interprétation climatique combinant analyse géochimique et données préliminaires acquises sur les thécamoebiens.

MOTS CLES: Tourbière du Misten, Hautes-Fagnes, Atlantique, Subboréal, Subatlantique, analyse pollinique, thécamoebiens, géochimie.

1. Introduction peat archives using palynology have already demonstrated their potential for reconstructing regional vegetation changes (e.g. Peatlands offer unique opportunities for high-resolution climate Persch, 1950; Dricot, 1960; Damblon, 1978, 1994). reconstruction. In the Hautes-Fagnes Plateau (Eastern Belgium), The saddle-raised Misten Bog (50°33´50´´N, 06°09´50´´E, culminating at 694 m a.s.l., peatlands cover 3750 ha, including 620 m a.s.l.), located in the Hautes-Fagnes Plateau, contains about 1000 ha of raised bogs protected since 1957 in a state some of the deepest peat deposits of this area, with more than nature reserve. The topographic conditions for areas where 7 m of peat in its centre (Fig. 1). The bog has been cut along its peat accumulates are given by Wastiaux et al. (2000). A general outer rim, mainly in the north-eastern and south-eastern edges. description of the Belgian peatland vegetation, in particular those Misten Bog sits on an isolated plateau that prevents the bog from of the Hautes-Fagnes, is provided by Frankard et al. (1998). receiving lateral mineral inputs, e.g. through small streams. The The Hautes-Fagnes are situated in a key position among vegetation on the site is mainly composed of Sphagnum ssp and European peat deposits, under both oceanic and continental Polytrichum strictum, built up into low hummocks, structured influences (Streel, 1959). Previous studies of the Hautes-Fagnes by Eriophorum vaginatum. Rare hollows are dominated by https://doi.org/10.20341/gb.2018.009 130 M. Streel, M. Paillet, J. Beghin, T. Leclef, M. Lamentowicz, K. Kamran, M. Court-Picon, M. Allan, N. Fagel & Ph. Gerrienne

Figure 1. (a) Location of the Misten peat bog in eastern Belgium, and (b) map of the Misten peat bog, modified from Allan et al. (2013). The colourings indicate the peat thickness as deduced from surface radar prospection (Wastiaux, 2002). The red dot shows the location of the MIS-08-01b core (this study), and the blue dot the probable location of the Hattlich pollen diagram of Persch (1950).

Eriophorum angustifolium, Narthecium ossifragum and a few (iii) to analyse and characterize the testate amoebae assemblages Rhynchospora alba. Hummocks are currently hidden by Erica of the Misten peat bog; tetralix, Calluna vulgaris and a few Vaccinium spp. shrubs, (iv) to test the application of three transfer functions, to interpret reflecting a recent drying trend (Streel et al., 2014). The site is the variations of the testate amoebae in terms of wetness also surrounded by Molinia coerulea. characteristics at the surface of the peat bog central area; Schwickerath (1937) and Persch (1950) carried out pollen (v) to integrate results based on pollen and testate amoebae in analyses (at 12 cm and at 5 cm intervals respectively) from order to propose a detailed biostratigraphy of the site. marginal sections of the Misten bog. Persch (1950) used Overbeck & Schneider’s (1938) classification of Holocene vegetation 3. Materials and methods landscapes to subdivide the pollen sequence (from their Boreal 3.1. Sampling, radiocarbon dating and chronology Subzone VII to Subatlantic Subzone XI). Additionally, he In February 2008, a peat core (MIS-08-01, 755 cm long) was introduced a quantitative approach based on Corylus abundance collected from the central part of the Misten site (Fig. 1). The (from their Boreal Subzone VII to Subboreal Subzone IX) top 100 cm were sampled by using a titanium Wardenaar corer defining 4 maxima CI, CII, CIII and CIV as well as on Fagus (Wardenaar, 1987) from the University of Heidelberg. Results on abundance (within their Subzone XI) defining 4 further maxima palynology and testate amoebae were published by Streel et al. FI, FII, FIII and FIV. He suggested that these fluctuations in (2014). The lower part (MIS-08-01b), sometimes named below Corylus and Fagus abundance could be used to date and correlate the “long core”, was cored with a Belorussian corer (Belokopytov between different regional pollen diagrams. This approach was & Veresnevich, 1955) and reached a depth of 7.5 m (Allan et al., subsequently used in the Hautes-Fagnes area by several authors 2013). (e.g. Dricot, 1960; Damblon, 1978; Streel et al., 2014). Radiocarbon ages were obtained on macrofossil samples (stems, branches or leaves of plant material) extracted under 2. Objectives of the study a binocular microscope. Nine samples were prepared at the The main objectives of the present work are: GADAM Centre (Silesian University of Technology, Gliwice, (i) to provide a palynological study at high resolution of the Poland) according to the protocol described by Piotrowska deepest area of the Misten peat bog (Hautes-Fagnes, Belgium); et al. (2011) and Piotrowska (2013). Radiocarbon dates (n = (ii) to compare our results with those obtained by Persch (1950) 15) obtained by acceleration mass spectrometry (AMS) were at the periphery of the Misten peat bog; processed using the “Bacon” software (Blaauw & Christen,

Table 1. Results of 14C dating for the MIS-08-01b peat core. Independently calibrated age ranges were obtained with the OxCal4 program (Bronk Ramsey, 2009), and the modelled ages were obtained after “Bacon” calculations (Blaauw & Christen, 2011). In both cases, the IntCal09 calibration curve was used (Reimer et al., 2009). See Allan et al. (2013, table 2). We have included data from Reimer et al. (2013, IntCal13) for comparison purpose although all these data are practically similar.

Sample Name Laboratory Depth (cm) Age 14C BP Modelled age range calBP (Intcal09) Modelled age range calBP (Intcal13) (94.5% probability) (94.5% probability) MIS-01/245 GdA-2230 286.17 298025 3075–3255 3070–3226 MIS-01/282 GdA-2231 340.77 347020 3650–3830 3649–3829 MIS-01/334 GdA-2232 408.03 377030 4000–4240 4000–4239 MIS-01/381 GdA-2233 474.25 430030 4830–4960 4829–4960 MIS-01/450 GdA-2234 568.80 505020 5740–5895 5739–5894 MIS-01/476 GdA-2235 603.00 521030 5910–6095 5909–6095 MIS-01/517 GdA-2236 658.80 568020 6410–6495 6409–6495 MIS-01/541 GdA-2237 690.00 594020 6680–6840 6679–6843 MIS-01/589 GdA-2238 741.38 623520 7025–7250 7027–7250 Early Atlantic to Early Subatlantic of the ombrotrophic Misten bog (Eastern Belgium) 131 2011) to establish an age–depth model as well as an age range for Mitchell, 2009), but this total was not reached for some samples. each slice of peat. The curve IntCal09 was used for calibration The relative frequency of each taxon was calculated and converted (Reimer et al., 2009; see also Reimer et al., 2013). The age–depth into a percentage of the total amount of the population. Samples model was calculated for 600 cm of the studied peat core. The with total count below the statistical threshold of 100 were not accumulation rate was set as a gamma distribution with a mean excluded from the dataset. Although this introduces statistical of 10 yr cm−1. The accumulation variability was set with a beta bias, it was chosen in order to avoid gaps in the diagrams distribution with strength of 4 and a mean of 0.7 (Allan et al., The diagram of the long core was drawn with the software 2013). Tilia (v.1.7.16, Copyright © 1991-2011 Eric C. Grimm). The The ranges of calibrated radiocarbon ages of dated peat taxa were clustered in three groups (1st = black, 2nd = medium layers involved in the present work (MIS-08-01b) are presented grey and 3rd = light grey) based on their overall weight (%), in Table 1. The age–depth model covering the period from ca. calculated for all the profile, and also sorted, from the left to 7300 cal BP to 2000 cal BP was published by Allan et al. (2013). the right, by alphabetical order. A biozonation scheme was The age model reveals a relatively constant peat accumulation applied to the diagrams to facilitate the qualitative description rate, with an average value of ca. 0.11 mm yr−1. Consequently, the and interpretation. Data were transferred in a spreadsheet with analysis of 1 cm thick sample represents ca. 9 years. minimum value criteria of 7. Consequently, assemblage biozones were based on taxa that have the highest relative frequency. A 3.2. Pollen analysis stratigraphically constrained cluster analysis by the method of 352 samples with known volume and weight were treated with HCl incremental sum of squares (CONISS, Grimm, 1987), (Tilia (10%) and submitted to KOH (10%). The residues were dissolved v1.7.16), with square-root transformation (Edwards & Cavalli- in 96% acetic acid and acetolysed (Faegri & Iversen, 1989). After Sforza’s chord distance) was applied. centrifugation, the solutions were filtered through 200 µm and 3.3.2. Calculation of the Shannon-Weaver Diversity index 12 µm mesh shieves. The isolated spores and pollen grains were The Shannon-Weaver Diversity index (Shannon & Weaver, then mounted in glycerin and counted up to a minimum of 300 1963), was calculated for the long section and defined as (Beisel (mean: 353) arboreal pollen grains excluding herbaceous pollen, et al., 2003): bryophyte and fern spores. Pollen identification was aided by Moore et al. (1991), Reille (1992, 1995, 1998) and Beug (2004). Counting was performed for 352 samples at 1.5 centimetre intervals. TILIA and TILIA GRAPH were used for diagrams conception based on percentages (Grimm, 1990). A TILIA diagram and a stratigraphically constrained cluster analysis by where H’ = code of the usual name (Shannon-Weaver Diversity incremental sum of squares method were generated (Grimm, index) in accordance with Smith & Wilson (1996), S = number 1987; CONISS in Fig. 2). of taxa in the community or species richness, and = relative 3.3. Testate amoebae analysis frequency of the ith taxon in the whole community, with Q = the 3.3.1. Data treatment total number of tests (all individuals for one level). 352 samples for testate amoebae analysis were prepared following 3.3.3. Transfer functions the recommendations of Booth et al. (2010). Testate amoebae Three transfer functions (Charman et al.; 2007 as described by were identified and quantified to the lowest possible taxonomic Sillasoo et al., 2007; Lamentowicz et al., 2008; Amesbury et al., level according to the dichotomous key proposed by Charman et 2016) have been used to assign hydroclimatic conditions to the al. (2000). At least 100 individual tests were counted (Payne & biozones identified with the CONISS analysis.

Figure 2. Evolution of the tree pollen rain on the Misten peat bog from the Atlantic up to the base of the Subatlantic. Silhouettes of Acer and Salix show 5x exaggeration of their percentage values. 132 M. Streel, M. Paillet, J. Beghin, T. Leclef, M. Lamentowicz, K. Kamran, M. Court-Picon, M. Allan, N. Fagel & Ph. Gerrienne 4. Results and discussion from a core. Indeed, Persch’s (1950) diagram stops more or less at 1800 AD suggesting, by comparison with the Misten area (Streel et 4.1. Pollen analyses al., 2014), that about 20 cm of superficial peat was inappropriate for 4.1.1. High resolution palynological analysis of the MIS-08-01b core pollen analysis, as often noted at the top of peat cutting. Moreover, Hattlich is 4 m deep, which corresponds to the depth of the peat Figure 2 (Kamran et al., 2016) shows the evolution of the arboreal bog at its periphery (see Fig. 1). Peat where MIS-08-01b was taken (or tree) pollen rain on the Misten peat bog between the Atlantic is more than 7 m thick, although covering a smaller time span and the base of the Subatlantic. The studied section begins at the as will be demonstrated later. That gives us a chance to compare depth of 753.5 cm in the Atlantic period and continues to the depth peat growth under slightly different ecological conditions, the two of 270 cm in the early Subatlantic period. In this time span, the tree studied areas being separated by a few hundred metres. pollen percentages were high (94-100%), suggesting highly closed Percentages of taxa in the Hattlich diagram were forest conditions in the surroundings, mainly consisting of trees calculated, as was often done during the last century, on the such as Alnus glutinosa, Corylus avellana, Quercus ssp. and Fagus sum of Arboreal Pollen (AP) without Corylus. This last taxon sylvatica. Four zones could be distinguished in the studied section can therefore reach very high percentages as shown in the including Atlantic a, Atlantic b, Subboreal and Subatlantic. In the Boreal period (VII) (a maximum of 287%, Fig. 4). To compare Atlantic a/Atlantic b zone-boundary, located at the depth of 600 cm, MIS-08-01b with the published Hattlich diagram, the sum the percentage of Tilia pollen exceeds that of Ulmus. The Ulmus of AP without Corylus was recalculated. The taxa taken into decline in the Atlantic b/Subboreal boundary, at the depth of 450 cm, consideration by Persch (1950) for correlation purpose are is possibly interpreted as resulting from human impact on the those used in the Overbeck & Schneider’s (1938) zonation landscape (Troels-Smith, 1960; Turner, 1962; Iversen, 1973; Peglar, (Table 2), i.e. Betula, Corylus, Fagus, the Quercetum mixtum 1993; Peglar & Birks, 1993; Hannon et al., 2000). Fagus sylvatica (sum of Quercus, Fraxinus, Tilia and Ulmus) and Pinus. appears in considerable proportion just from the beginning of the Persch obviously added Alnus to emphasize the start of the Subboreal and shows a sharp increase at the start of the Subatlantic “Betula peat” (his “Birkenbruchtorf”; Fig. 4) in a rather wet period. Non arboreal pollen diagram (Fig. 3; Kamran et al., 2016) environment of the Boreal Corylus/Ulmus forest. The base shows less than one percent of diverse taxa where one can notice the of the MIS-08-01b profile did not reach such environment, first occurrence ofPlantago lanceolata type starting in the upper part perhaps because the drilling system could not penetrate the of the Atlantic b period and the more accentuated presence (around woody (?) substrate. The base of the profile reached the one percent) of Poaceae in the upper part of the Subboreal period. minerotrophic part of the peat bog (Salpeteur, 2011). Pollen These probable anthropogenic markers are present in low quantities. rain of Alnus, Betula and Pinus was not used for correlation in This is probably the result of long transport by the wind and does the present paper. On Figure 4c, Pinus, always less than 5%, not presumably indicate any evidence of anthropic activity in the is even omitted. We emphasize the ratio Tilia versus Ulmus proximal surrounding of the peat bog. (Fig. 4a), a useful character in the lower half of both diagrams, and the percentages of Corylus (Fig. 4b), more useful in the 4.1.2. Comparison between MIS-08-01b and Hattlich diagrams upper half. The Fagus/Quercetum mixtum (= QM) competition a) General considerations (Fig. 4c) is essential to show the change of the climate near the We do not know exactly where Persch (1950) collected his samples, top of the diagrams. but he writes they come from about 500 m south of the Eupen- Monschau road, at 620 m a.s.l., which means more or less at the b) Comparison of available ages of selected tie-points in four intersection of the track giving access to the Misten, the old trace of localities the cutting front and the related level curve (Fig. 1). We think that We selected nine tie-points recognizable in both diagrams the Hattlich material came probably from a cutting trench and not (Table 3). They are retained from the Persch’s Hattlich diagram

Figure 3. Non arboreal pollen diagram showing the taxa represented by less than one percent (from Kamran et al., 2016). Silhouettes show 20x exaggeration of their percentage values. Early Atlantic to Early Subatlantic of the ombrotrophic Misten bog (Eastern Belgium) 133

Figure 4. Comparison of Hattlich (Persch, 1950) and MIS-08-01b (this study) pollen data. Figure Atlantic/Subboreal limit suggested at tie-point 5. 1) with modelled age range (94.5% probability). Table (see Ages are given in calBP without Corylus . Position of the 9 tie-points is recognized in both diagrams. AP All data based on The Misten diagram obviously does not reach the Boreal/Atlantic limit observed in Hattlich diagram. 134 M. Streel, M. Paillet, J. Beghin, T. Leclef, M. Lamentowicz, K. Kamran, M. Court-Picon, M. Allan, N. Fagel & Ph. Gerrienne

Table 2. Floristic and climatic characteristics in Periods Vegetation characteristics the Hautes-Fagnes deduced by Persch (1950) Fagus prevailing on Corylus and on the Quercetum mixtum from Overbeck & Schneider’s (1938) zonation. XI - Subatlantic Less warm than periods VII to X X - Subboreal Quercus and Fagus phase of the mixed Quercus-Corylus forest Late warm period Starting pejorative change of the climate Regression of Corylus, Ulmus and Tilia Fagus reaching Quercetum mixtum values IX - Subboreal Quercus phase of the mixed Quercus-Corylus forest Late warm period Start of the continuous presence of Fagus Fagus becoming more abundant in the upper part (>5%) Corylus more abundant than below (=CIII) (CIV) VIII - Atlantic Ulmus and Tilia phase of the mixed Quercus -Corylus forest Middle warm period First occurrence of Fagus Tilia prevailing on Ulmus (VIIIb) Ulmus and Tilia phase of the mixed Quercus -Corylus forest Corylus reaching 100% (=CII) Ulmus prevailing on Tilia (VIIIa) VII - Boreal Corylus >> 100% (CI) Early warm period Betula, Pinus abundant but decreasing Quercetum mixtum more and more abundant Ulmus reaching a maximum of 26% and from the characteristics used by Overbeck & Schneider’s to Paillet’s (2016) work (Table 4), corresponding respectively to (1938) zonation. the top Corylus CIII and to the intersection between QM and Fagus curves. Table 3. Tie-points retained from the Persch’s (1950) Hattlich diagram Tie-points (TP) were also used by Litt et al. (2009) in the and from the characteristics deduced from Overbeck & Schneider’s Westeifel Volcanic Field (50 km south-east of the Hautes- (1938) zonation. Fagnes plateau), to correlate between Holz Maar and Meerfelder Maar varved sequences. We identified there three tie-points Tie-points Characteristics corresponding respectively to tie-points 2 (TP6 or after Ulmus TP 9 Top: Fagus/Quercetum mixtum co-dominant decline), 4 (TP7 or base of Fagus continuous curve), and 7 (TP8 or last Corylus peak before increase of Fagus). Tie-point 4 (base of Base: Fagus >40% (=about base: XI) Fagus curve) shows the larger difference of age between Hautes- TP 8 Base: Fagus /Quercetum mixtum co-dominant Fagnes Plateau and Westeifel. The base of Fagus continuous TP 7 Top: Corylus CIV (=about base X) curve is indeed very difficult to identify as shown in the MIS-08- TP 6 Top: Corylus CIII - Base: Fagus >5% 01b diagram (Fig. 4), but one must also take into consideration the TP 5 Base: Corylus CIII (=about base IX) possible difference of migration speed of the taxon across Middle TP 4 Base: Fagus Europe during the Atlantic period (Schmidt, 1995; Giesecke et al., 2007). Tie-points 2 (top of Ulmus dominance) and 7 (top of Base: Tilia dominance (=about base VIIIb) TP 3 Corylus peak) seem to be more reliable than tie-point 4. TP 2 Top: Ulmus dominance TP 1 Top: Corylus CI (=base VIIIa) c) Analysis of intervals between tie-points in MIS-08-01b and Hattlich diagrams Between tie-points 1 and 3, the most abundant group of taxa (the Age data given by Persch (1950) on the Hattlich diagram Quercetum mixtum) fluctuates around 60%, Alnus around 30%, (Fig. 4) result from extrapolation (about 50 cm of peat/1000 years Betula around 5% (Fig. 4). The Quercetum mixtum is however or about 1 cm/20 years) below the then accepted age of 600 BC not homogeneous: Ulmus prevalence on Tilia is less and less for the base of the Subatlantic. These data are here transformed obvious from 1 to 3. Corylus fluctuates between 60% and 80%, (Table 4) in BP ages (by arbitrarily adding 1950 years) to except near the base of the MIS-08-01b where it may reach 100% facilitate the comparison with the Misten 01 data where we use (maybe representing the CII of Persch, 1950) and in the upper part 14C modelled age ranges with 94.5% probability and where the of interval 2-3 in the Hattlich diagram where that taxon fluctuates analysis of 1 cm thick sample represents ca. 9 years. between 40% and 60%. The interval between tie-points 1 and 3 Tie-points were also used to correlate the Hattlich diagram corresponds to the lower part (VIIIa) of the Atlantic period. with a diagram made in the Rurhof peat bog, about 10 km south Between tie-points 3 and 4, the Quercetum mixtum fluctuates (Paillet, 2016). Consequently, tie-points 6 and 8 were dated thanks between 40% and 60% in the MIS-08-01b diagram, this probably

Table 4. Comparison of tie-point ages. BP ages for Hattlich or Westeifel are BC ages + 1950 yr.

Climatic zones Tie-points Hattlich BC Hattlich BP Misten calBP Rurhhof calBP Westeifel calBP About base XI Top Fagus /QM co-dom., base Fagus >40% 9 About 650 About 2600 3075-3255 About 2700 X base Fagus /QM co-dom. 8 About 850 About 2800 3275 2994-3166 ? About base X Top Corylus CIV 7 About 1150 About 3100 About 3650-3830 About 3840-3820 IX Top Corylus CIII, base Fagus >5% 6 About 1700 About 3650 About 4000-4240 4080-4235 ? About base IX Base Corylus CIII 5 About 2200 About 4150 About 5600 VIIIb Base Fagus 4 About 2700 About 4650 5478 ? About base VIIIb Base Tilia dominance 3 About 4000 About 5950 5910-6095 ? VIIIa Top Ulmus dominance 2 About 4800 About 6750 6410-6495 About 6250-6170 Base VIIIa Top Corylus CI 1 About 6000 About 7950 About 8550 Early Atlantic to Early Subatlantic of the ombrotrophic Misten bog (Eastern Belgium) 135 being the result of a marked regression of Ulmus. The slight more open vegetation (heath) in the centre allowing to “capture” increase of Betula and Alnus is only the counterpart of the there more pollen grains transported by wind than the presumably decreasing value of the Quercetum mixtum. Nothing comparable more forested periphery where local pollen rain was dominant. The is observed in the Hattlich diagram. distribution of Calluna vulgaris (Fig. 4) offers some possibility to Between tie-points 4 and 5, the Quercetum mixtum fluctuates evaluate the density of the shrub cover in the centre of the peat bog around 50% in the MIS-08-01b diagram, around 60% in the and on its periphery. Between tie-points 1 and 3 (VIIIa Atlantic Hattlich diagram. Tilia and Ulmus values decrease from 4 to 5 period), Calluna never reaches 10% in the periphery but often (from less than 10% to less than 5%) in the MIS-08-01b diagram, more than 10%, reaching sometimes almost 20%, in the centre of but again nothing comparable is observed in the Hattlich diagram. the peat bog. Between tie-points 3 and 4 (VIIIb Atlantic period, A continuous curve of Fagus is situated in the mid-Atlantic during the strong reduction of Ulmus), Calluna density is almost VIIIb in the MIS-08-01b and begins to be clearly visible around similar in both environments. However, between tie-points 4 and 5, 540 cm, corresponding to tie-point 4. The interval between a strong reduction (5-10%) of Calluna occurs only in the centre of tie-points 3 and 5 corresponds to the upper part (VIIIb) of the the peat bog. From tie-points 5 to 9 (Subboreal period) abundance Atlantic period. of Calluna is again very similar in both environments, being more Between tie-points 5 and 6, the Quercetum mixtum fluctuates and more reduced from tie-points 6 to 9. These data probably around 50% in both diagrams. Corylus values reach more than reflect local changes in the centre of the peat bog. 80% in the Hattlich diagram, from 100% to 160% in the MIS-08- 01b diagram (the CIII of Persch, 1950). 4.2. Testate amoebae analyses Between tie-points 6 and 7, the characteristics are more or 4.2.1. Testate amoebae zonation and Shannon-Weaver Diversity less similar to interval 5 and 6, including a possible CIV (Persch, Index 1950), except a major feature arising at tie-point 6 with the increasing, but irregular, development of Fagus (between 5% and The stratigraphically constrained cluster analysis resulted in the 30% in the MIS-08-01b diagram) starting the competition with identification of five biozones (biozones A to E). The Shannon- the Quercetum mixtum. Weaver Diversity Index was calculated for all samples. The The interval between tie-points 5 and 7 corresponds to the variation of the Shannon-Weaver Diversity Index along the core lower part (IX) of the Subboreal period. is presented at Figure 5. Between tie-points 7 and 8, Fagus fluctuates between 10% Biozone A (753.5 cm = 5300 BC/7250 BP to 662.58 cm = and 20% in both diagrams. 4576 BC/6526 BP) displays high-amplitude fluctuations that Between tie-points 8 and 9, the competition between Fagus seem to be alternating for both Archerella (Amphitrema) flavum and the Quercetum mixtum reach a maximum, both oscillating and Difflugia pulex (Fig. 6). High value of the Shannon-Weaver’s between 20% and 40%. Corylus decreases below 60% (between Diversity index occurs at the top of the biozone A. 40% and 60% in the MIS-08-01b diagram, between 30% and Biozone B (662.58 cm = 4576 BC/6526 BP to 535.68 cm = 40% in the Hattlich diagram). 3528 BC/5478 BP) is dominated by Difflugia pulex; Archerella The interval between tie-points 7 and 9 corresponds to the (Amphitrema) flavum however displays a high relative frequency upper part (X) of the Subboreal period. (47%) at approximately the middle part. Within this biozone, Tie-point 9 indicates the base of fluctuations ofFagus between testate amoebae reach a first taxonomic plateau of the Shannon- 30% and 60% and a strong decrease of the Quercetum mixtum Weaver Diversity index. below 20%. It corresponds to the base of the (XI) Subatlantic Biozone C (535.68 cm = 3528 BC/5478 BP to 415.609 cm period. = 2263 BC/4213 BP) is dominated by Archerella (Amphitrema) flavum; Difflugia pulex however displays also a high relative d) Major discrepancies between Hattlich and Misten diagrams frequency (50%) at approximately the middle part and three others Based on the comparison of Hattlich and Misten sites (Table 5), at the upper part. Within this biozone, a second taxonomic plateau we conclude that the central part of the peat bog (Misten site) of the Shannon-Weaver Diversity index starts to be reached. received more Corylus pollen grains and less QM pollen grains According to Allan et al. (2013), a very high humification rate (= than the periphery (Hattlich site). Such observation may reflect a 78%) occurs at approximately 3000 BC/ 4950 BP.

Table 5. Comparison of pollen diagrams discrepancies between Hattlich (Persch, 1950) and Misten (this study).

Tie-points intervals Hattlich Misten

Interval 8-9 Corylus 30-40% Corylus 40-60%

Interval 5-6 Corylus >80% Corylus >100 to 160%

Interval 4-5 QM 60% Tilia -Ulmus stable QM 50%, fall of Tilia-Ulmus 10% to 5%

Interval 3-4 QM 50-60% Fall of QM (40-60%) and Ulmus

High interval 2-3 Corylus 40-60% Corylus 60-80%

Figure 5. Shannon-Weaver Diversity index (based on testate amoebae). The Shannon-Weaver Diversity index is smoothed by a fifth-degree polynomial curve. Header shows biozones (A to E) defined by using CONISS (Grimm, 1987) in Fig. 6. 136 M. Streel, M. Paillet, J. Beghin, T. Leclef, M. Lamentowicz, K. Kamran, M. Court-Picon, M. Allan, N. Fagel & Ph. Gerrienne in MIS-08-01b. . Pollen tie-points 1 to 9 are added for comparison purpose with Fig. 4. purpose with for comparison added 9 are 1 to tie-points . Pollen flavum (Amphitrema) Archerella flavum read of Amphitrema Instead tests. of 100 counted threshold statistical the reached have not that samples the Grey dots indicate Figure 6. Distribution of selected testate amoebae Figure Early Atlantic to Early Subatlantic of the ombrotrophic Misten bog (Eastern Belgium) 137 Biozone D (415.61 cm = 2263 BC/4213 BP to 305.56 cm this biozone. Arcella discoides type is missing in biozone D except = 1326 BC/3276 BP) is not clearly dominated by Archerella at the top. At the upper part of this biozone the second taxonomic (Amphitrema) flavum or Difflugia pulex. Difflugia pulex tends plateau of the Shannon-Weaver Diversity index is reached. to decrease throughout the biozone. Two peaks of Amphitrema Biozone E (305.56 cm = 1326 BC/3276 BP to 141.1 cm wrightianum are obvious at the top. Cyclopyxis arcelloides type = 155 BC/2105 BP) is characterized by (i) a new composition fluctuates but never exceeds more than 15%. Difflugia pristis has of the testate amoebae assemblage with a high overall value a lower relative frequency than in lower zones. Hyalosphenia of the Shannon-Weaver Diversity Index, (ii) the lower relative subflava presents a little but obvious positive shift. Relatively larger frequency (%) displayed by Difflugia pulex compared with the positive shifts are also displayed by Bullinularia indica, Nebela underlying biozones, (iii) the presence, with higher relative militaris, Trigonopyxis arcula sensu lato, Hyalosphenia papilio frequency, of alternating Hyalosphenia subflava and Amphitrema and Trigonopyxis arcula minor at approximately the middle part of wrightianum and (iv) the obvious positive shifts of Arcella

Figure 7. Distribution of selected testate amoebae in according to the data issued from the transfer function of Amesbury et al. (2016). Range and optimal distance of these taxa above the water-table (WT). Red lines position, deduced from CONISS analysis, is almost identical to subdivisions A to E in Fig. 6 except for the C/D limit.

Figure 8. Distance of testate amoebae to water- table for the MIS-08-01b. The curves of the depth to water-table (in cm) were inferred by using three testate amoebae transfer functions : 1, from Charman et al. (2007); 2, from Lamentowicz et al. (2008); 3, from Amesbury et al. (2016) in Fig. 7. Header shows biozones (A to E) defined by using CONISS (Grimm, 1987) in Fig. 6. 138 M. Streel, M. Paillet, J. Beghin, T. Leclef, M. Lamentowicz, K. Kamran, M. Court-Picon, M. Allan, N. Fagel & Ph. Gerrienne discoides type, Cyclopyxis arcelloides type and Nebela militaris shown by the first occurrences of Cyclopyxis arcelloides type at approximately the middle part; Trigonopyxis arcula sensu lato and the start of the progressive decreasing of Difflugia pristis is also present. (Fig. 6). However, the percentages of Difflugia pristis in the upper From the base to the top of the entire long core, the relative part could be underestimated because this species is sometimes frequency of Assulina muscorum globally increases with major difficult to identify amongst organic debris. According to Allan peaks of high relative frequency (> 40 %) in the biozones C, D et al. (2013) and Wanner et al. (2011), the time intervals between (two at the bottom) and E. 3200 and 2500 BC (or 5150 and 4450 BP) are characterized by 4.2.2. Palaeo-hydroclimatic conditions of testate amoebae biozones wet climatic conditions. a) General considerations Biozone D The water-table depth optima and tolerances for the taxa used Biozone D is interpreted as a climatic transition interval are presented at Figure 7, on the basis of the data of figure 5 (with high taxonomic diversity) as shown by the decrease of of Amesbury et al. (2016). This diagram emphasizes the rather Difflugia pulex and Difflugia pristis but also with the increase dry character of the Atlantic VIIIb and Subboreal IX and X, the of Amphitrema wrightianum, Hyalosphenia subflava, Nebela majority of taxa selected being in the optima ranges living 10 to militaris, Trigonopyxis arcula sensu lato, Hyalosphenia papilio 20 cm above the WTD, reaching sometimes 20 to 30 cm above and Trigonopyxis arcula minor. The end of this climatic transition the WTD (Fig. 7). The wet character of the Subatlantic XI is is obvious at the top of this biozone (at the transition from emphasized by taxa like Amphitrema wrightianum type living biozone D to biozone E) where Difflugia pulex reaches very 0-5 cm above the WTD or Arcella discoides and Argynnia vitraea low percentage of relative frequency (Fig. 6). During this period living 5-10 cm above the WTD. Additionally, Amphitrema of time the population of Archerella (Amphitrema) flavum and wrightianum is noted by Amesbury et al. (2016) as “skewed” to Difflugia pulex alternate rapidly, with low differences between the Atlantic region, when most of the other taxa are “skewed” them; it is consequently difficult to safely qualitatively infer to the Continental region. Its high abundance at the base of the the bog surface wetness. Thanks to the three transfer functions, Subatlantic XI might be considered the result of a significant drier climatic conditions could be assigned to this biozone. At general change in the local climate of the Hautes-Fagnes Plateau. least three short events of driest conditions, with relative high In order to assign climatic characteristics to the five above- amplitude, occurred at approximately 2238.3 BC/4188.3 BP, defined biozones, three transfer functions (Charman et al., 2007 2018.5 BC/3968.5 BP and 1798.8 BC/3748.8 BP, as shown by as described by Sillasoo et al., 2007; Lamentowicz et al., 2008; Difflugia pulex (Fig. 6). According to Allan et al. (2013) the time Amesbury et al., 2016) have been applied. The results of the intervals [2500-2000 BC/4450-3950 BP (transition between three transfer functions are broadly comparable (Fig. 8). biozone C to biozone D) and 2200-1800 BC/4150-3750 BP] are characterized by dry climatic conditions. b) Detailed description of the palaeo-hydroclimatic conditions of the five biozones Biozone E Biozone E is characterized by the end of a climatic transition Biozone A displayed by testate amoebae assemblage (mainly by Difflugia A preliminary geochemical study (Salpeteur, 2011) showed pulex, Amphitrema wrightianum and Hyalosphenia subflava) that the fen-bog transition (FBT) started at 687 cm depth (mode ≈ with an overall high Shannon-Weaver Diversity index (Figs 5 4773.5 BC/ 6723.5 BP) to finish at 663 cm (mode ≈ 4575.9 and 6). Thanks to the three transfer functions, wetter climatic BC/6525.9 BP), which is the top of the biozone A (Fig. 6). Because conditions could be assigned to the lower part of this biozone ombrotrophic mires receive water mainly from atmospheric and drier climatic conditions could be assigned to the upper part precipitation, the depth to water-table is linked to hydroclimatic of this biozone. Very high amplitude of water-table fluctuations conditions; on the other side, minerotrophic mires have significant occurred over this period of time (Figs 7 and 8). Two wet shifts input of water from surface runoff and groundwater (Charman, are obvious at the lower part of this biozone at ≈ 1243 BC/3193 1997). Because biozone A includes the minerotrophic part of BP and 932 BC/2882 BP, as shown by Archerella (Amphitrema) the extant peat bog, palaeo-hydroclimatic conditions could with flavum. At least, one short event of driest climatic conditions less certainty be assigned to this biozone as can be done for the occurs at around 700 BC/2650 BP, as shown by Hyalosphenia stratigraphically upper ombrotrophic part. At the upper part of subflava (Fig. 6). According to Allan et al. (2013), the time the biozone A, testate amoebae reach a first plateau of taxonomic interval [1200-600 BC/3150-2550 BP] is characterized by dry diversity with a very high index of the Shannon-Weaver Diversity climatic conditions. followed by an important dropdown (Fig. 5).This high amplitude difference could be due to the transition from minerotrophic to 4.2.3. Testate amoebae zonation based on dominant species and ombrotrophic conditions. Wetter surface conditions are proposed related humidity on the peat bog surface for the biozone A by using the three testate amoebae transfer The species with the highest overall relative weight (%) along functions. According to Allan et al. (2013), the time interval [5300- the entire profile areArcherella (Amphitrema) flavum (suggesting 4700 BC/7250 BP-6650 BP] is characterized by wet climatic wet conditions) and Difflugia pulex (suggesting drier conditions). conditions (but see remarks above about the palaeo-hydroclimatic The numbers of representatives of the two species seem to conditions in minerotrophic mires). vary synchronously but in an opposite way, even though these Biozone B species have non-significant negative linear correlation (r= -0.4). Drier climatic conditions can globally be assigned to Accordingly, we tentatively use their respective abundance as biozone B. However, at least, one short wetter event with a indicative of wet (dominance of Archerella (Amphitrema) flavum) relatively high amplitude (mode ≈ 4142.9 BC/6092.9 BP) occurs or dry (dominance of Difflugia pulex) conditions. Assulina at the middle part of the biozone B, as shown by Archerella muscorum has also high overall relative weight, but lower than (Amphitrema) flavum(Fig. 6). According to Allan et al. (2013) the that of the species above mentioned. time interval [4700-4000 BC/6650 BP-5950 BP] is characterized 4.2.4. Integration of testate amoebae and pollen zonations by dry climatic conditions. Integration of the two zonations permits the subdivision of Biozone C the ombrotrophic part of the studied section into 18 smaller Wetter climatic conditions can globally be assigned to time intervals (Table 6; Fig. 9) with various pollen features biozone C with, at least, a short drier event with a relative high corresponding to detailed humidity condition “registered” by the amplitude (≈ 2880.8 BC/4830.8 BP) at the middle part, as shown testate amoebae on the peat bog surface at each of the studied by Assulina muscorum, and drier conditions at the upper part time intervals. As no significant anthropic actions could be with, at most, two short drier event with a relative high amplitude demonstrated on and around that peat bog during that time span, (≈ 2571.2 and 2423.9 BC/4521.2 and 4373.9 BP), as shown by it is assumed here that variations of humidity at the surface of Difflugia pulex (Fig. 6). Nonetheless, it has to be noted that, the peat bog reflect also indirectly variation in general climatic within this biozone, there is the start of a climatic transition as conditions on the surrounding area. Early Atlantic to Early Subatlantic of the ombrotrophic Misten bog (Eastern Belgium) 139 ). Time intervals as intervals Time flavum ). (Amphitrema) Archerella from Allan et al. (2013). The testate amoebae were classified according to their affinity with wet conditions. The three vertical dark blue bars show the cold events cold the show bars blue dark vertical three The conditions. wet with affinity their to according classified were amoebae testate The (2013). al. et Allan from

Figure 9. Comparison of the Misten proxies (pollen, dust flux, εNd, humification, and testate amoebae). Figure flavum read of Amphitrema Fig. 6 (instead from area, Hautes-Fagnes the in periods Atlantic–Subboreal in amoebae testate main Two Fig. 4. from of tie-points characteristics Pollen deduced from Table 6. Dust flux, εNd, humification, and testate amoebae testate and humification, εNd, flux, Dust 6. Table from deduced cation model is from Claussen et al. (1999). Water-table (WT) (cm) are reproduced from Fig. 7. Water-table The Saharan deserti fi cation model is from Claussen et al. (1999). and the three light blue bars show uncertainty in length of cold events. et al. (2011) Wanner according to 140 M. Streel, M. Paillet, J. Beghin, T. Leclef, M. Lamentowicz, K. Kamran, M. Court-Picon, M. Allan, N. Fagel & Ph. Gerrienne

Table 6. Testate amoebae, pollen zones, time-intervals, dates comparisons. Ages cal BP from Table 1, and Figs 4 and 6.

The analysis of these 18 time intervals gives interesting testate amoebae and the better representation of heathlands in information on the behaviour of some taxa in response to climatic pollen diagrams from the area (Damblon, 1994), show slightly fluctuations. Increasing values of Tilia are noted in dry to driest drier local environments met by time-intervals 17 and 15, conditions from the Atlantic (VIIIa and VIIIb) to the Subboreal suggesting a rather dry climate with an increase of Tilia proportion IX, a situation met with Calluna on the peat bog in Atlantic VIIIb in the local QM Atlantic vegetation. The definitive dominance of and Subboreal IX (Fig. 4). Corylus values increase with dry/ Tilia on Ulmus (near 6000 cal BP) separates the Atlantic VIIIa driest conditions in Subboreal IX, but decrease with the same and the Atlantic VIIIb periods. These dry conditions might reflect conditions in Subboreal X. Fagus increases in dry conditions of the cooling event noted in Wanner et al. (2011) from 6500 to 5900 Subboreal IX and X but also in wet conditions of Subboreal X cal BP. A brief episode of wetter conditions (time-interval 16) has and Subatlantic XI. Ulmus increases and decreases indifferently little impact on this QM drier Atlantic vegetation. During this in dry and wet conditions during the Atlantic (mainly VIIIb), interval, there is no significant change in the dust flux intensity giving some support to the existence of an anthropic effect on the but the relatively dry conditions promote the erosion of local distribution of this taxon (See 4.1.1). soils. Between 8000 and 5500 cal BP, the Sahara aridification increases and the Saharan vegetation cover decreases. Then the 4.3. Mineral dust analysis available terrigenous material increases (Claussen et al., 1999; de Based on dust flux data from Allan et al. (2013), the climate Menocal et al., 2000; Bout-Roumazeilles et al., 2013). imprint in the Misten record during Mid- and Late Holocene and (iii) During the period from 5500 to 2550 cal BP, the Misten especially for two dust enriched intervals (5150 to 4750 cal BP dust flux increases compared to the mean value in the previous and from 2750 to 2550 cal BP) is evaluated (Fig. 9). intervals. At 4700 cal BP, time-intervals 12 (and 13?) suggest a (i) Peat growth at the Misten site starts at ~7300 cal BP, rather wet climate with adequate local QM Atlantic vegetation, and becomes ombrotrophic from 6700 cal BP. Damblon (1994) corresponding with a positive humidity anomaly at the scale of the pointed to the wet and warm climate of the Atlantic VIIIa period northern hemisphere between 4800 and 4600 cal BP as described (6500 cal BP- 6000 cal BP; partially met by time-intervals 18 and in Wanner et al. (2011). These time-intervals are characterized by 16), which is consistent with the warmest period of the Holocene wet local conditions underlined by the high wet testate amoebae described in Greenland by Johnsen et al. (2001) (see also Davis content and the low humification degree. The humid conditions are et al. (2003)). in agreement with the plant cover changes of the Hautes-Fagnes (ii) From 6700 to 5500 cal BP, the dust flux and humification Plateau deduced from palynology (Damblon 1994) (i.e. local remain relatively constant. The decrease in percentages of wet increase in hygrophilous and aquatic pollen taxa). Between 4500 Early Atlantic to Early Subatlantic of the ombrotrophic Misten bog (Eastern Belgium) 141 and 4000 cal BP, the general decrease of wet testate amoebae and values of Tilia are noted in dry to driest conditions from the the increase of the humification degree both indicate a drier local Atlantic (VIIIa and VIIIb) to the Subboreal IX. Ulmus increases environment, starting with time-interval 11. The observed increase and decreases indifferently in dry and wet conditions during the in dust flux may relate to important local erosion. The glaciers retreat Atlantic (mainly VIIIb) giving some support to the existence of in Europe from 4200-3800 cal BP (Mayewski et al., 2004) and the an anthropic effect on the distribution of this taxon. The definitive lake level minima (Magny, 2004) confirm a dry interval which is dominance of Tilia on Ulmus (near 6000 cal BP) separates the correlated with the first Subboreal (IX) period characterized by Atlantic VIIIa and the Atlantic VIIIb periods. These dry conditions Corylus developments (time-intervals 8 and 6), and the last Tilia might reflect the cooling event noted in North America (Residual increase (time-intervals 9 and 7). Between 3700 and 3200 cal BP, Laurentide Ice Sheet) from 6500 to 5900 cal BP. the second Subboreal (X) period shows a progressive change from dry (time-intervals 5 and 4) to wet conditions (time-interval 3, with 6. Acknowledgements Fagus starting dominance in the QM forest). Between 3200 and We are very grateful to Bernard Owens (Nottingham) who 2550 cal BP, the dust flux increases and reaches its maximum value improved the language of our manuscript and for his constructive in the core. The humification degree decreases and wet testate remarks. We also thank the referee, Freddy Damblon (Brussels) amoebae strongly increase. The regional pollen data indicates a for his detailed remarks and comments. We are grateful also to strong expansion of beech forests at the expense of the mixed oak Marcela Mezzatesta-Giraldo for her technical assistance. woodlands, whereas alders and birches developed again near and on wetlands. These changes point to a climatic deterioration with 7. 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